It Depends wether you have an iPad 2 3G + wifi or an iPad 2 wifi
If I were you and I had the 3G option, I would switch carriers to Vodafone and get a new sim
If you have the wifi only model, then I'm sorry, I can't help!!
If you have a smartphone they usually have that capability, some carriers charge extra for it though, usually in the $20-$30 range. If you have an android or iPhone you can root or jailbreak it to get this feature.